Extended analysis of solid cancer incidence among nuclear industry workers in the UK 1955-2011: comparison of workers first hired in earlier and later periods.

To address points arising from the recent study of nuclear workers in the USA and the International Nuclear Workers Study (INWORKS), concerning the difference in solid cancer risk estimates between those first hired in earlier and later calendar years, subsidiary analyses were conducted on a cohort of 172 452 workers in the National Registry for Radiation Workers (NRRW) from the UK. A total of 18 310 incident first primary solid cancer cases were registered in the period from 1955 until 2011 in the NRRW cohort and workers accrued 5.25 million person-years of follow-up. Incidences rates of all solid cancers combined, lung cancer and solid cancer excluding lung cancer were examined in terms of external radiation doses in the full cohort and in a sub-cohort of workers who had no record of internal exposure monitoring and were defined by the periods of first hire before and after the beginning of the years 1960, 1965 and 1970. All analyses were carried out using Poisson Regression. These analyses demonstrated that only for lung cancer between the pre-1965 and post-1964 periods is there strong evidence for a difference in the risks using the NRRW full cohort. In the other calendar period breakdowns and for the other cancer groups, there is no clear evidence of differences in the risks. The NRRW estimation of risks between recent and early workers is not generally consistent with the US workers cohort or the INWORKS evaluations that later hired workers are at much higher solid cancer risk than earlier hired workers, although INWORKS contains a significant part of the latest updated NRRW cohort as well as the US data. The conclusion that the INWORKS and US study data demonstrate a real difference in excess solid cancer risk from external radiation exposure between earlier and later workers is premature. The results presented here should also be treated with caution because of the limited corroborating evidence from other published studies. Information on internal doses, neutron doses as well as non-radiation factors such as smoking and asbestos exposure would be needed to make definitive inferences.